1. Field of the Invention
The present invention relates to a gate valve, and more particularly to a novel technique for effecting the opening and closing of a large opening for conveyance of a large member such as a liquid crystal panel in a non-sliding manner and with ease.
2. Description of the Related Art
JP 08-42715 A and JP 10-10834 A disclose conventional examples of such a gate valve for large openings.
In the example shown in FIG. 14A through 14C, a construction is adopted, in which a valve plate provided on a valve rod is laterally tilted.
In this example, only one of openings 2 and 3 of a valve box 1 is opened and closed by using one side of a single valve plate 90, and tilting movement and vertical movement of a valve rod 4 are effected by means of a complicated cam.
The conventional gate valve, constructed as described above, has the following problem. That is, since the vertical movement and tilting movement of the valve rod are effected by means of a complicated cam, a rather complicated cam mechanism is involved. Further, the valve plate, provided for an opening of a large valve box, has a large weight, resulting in a large valve size and high cost.
Further, since the opening is opened and closed by using solely one side of the valve plate, it is rather difficult to maintain the durability of the O-ring, which means that it is not easy to attain the requisite level of reliability and that the maintenance cost is rather high.